1. Field of the Invention
This invention relates to a method for preventing degradation of a liquid developer for electrostatic recording caused by contacting with paper and further to photosensitive paper, electrostatic recording paper and transfer paper.
2. Description of the Prior Art
Heretofore, various electrostatic recording methods utilizing liquid development have been known. For example, there may be mentioned a method comprising developing electrostatic latent images formed on a ZnO photosensitive paper with a liquid developer, a method comprising developing electrostatic latent images formed on an electric charge retaining layer of an electrostatic recording paper with a liquid developer, and a method comprising developing electrostatic images formed on a selenium photosensitive layer or an insulative layer with a liquid developer and then transferring the developed images in the presence of a carrier liquid.
In the electrostatic recording methods as mentioned above, the liquid developer inevitably contacts the photosensitive paper, electrostatic recording paper, or transfer paper in the developing step or transferring step. In general, the liquid developer having contacted the paper is recovered and used again for the subsequent development. During repeated use of the liquid developer, it is deteriorated and results in lowering image density and finally it can not be used any more. Such degradation is remarkable when a negatively chargeable liquid developer is used.
In general, a liquid developer for electrostatic recording contains dye, pigment, a fixing agent, a dispersing agent, a charge control agent and the like in a highly insulating carrier liquid in a form of dispersion or solution, and it is known that the liquid developer is deteriorated due to degradation of such materials by oxidation and heat.
It has been found that the degradation due to the repeated use of the liquid developer is still caused in the electrostatic recording methods comprising contacting a paper with a liquid developer even when a liquid developer containing materials which are not easily degraded is used.
The present inventors have found as the result of chemical analysis of the liquid developer deteriorated by repeated use that a substance accelerating the degradation sheds into the carrier liquid from the photosensitive paper, electrostatic recording paper and transfer paper.